1. Field of the Invention
The present invention is related to a resin formulation useful for vacuum resin infusion molding processes, wherein the resin formulation is based on a divinylarene dioxide.
2. Description of Background and Related Art
It is well known to use epoxy resins in vacuum resin infusion molding processes. A vacuum resin infusion molding process requires epoxy resin formulations having low viscosity for example less than 300 mPa·s at 25° C. However, conventional epoxy resins typically have a viscosity higher than 300 mPa·s at 25° C.; and therefore, when a conventional epoxy resin is used in a vacuum resin infusion molding process, a reactive diluent is typically needed and added to the conventional epoxy resin to lower the viscosity of the epoxy resin and achieve the required low viscosity in order for the conventional epoxy resin formulation to be useful in the vacuum resin infusion molding process.
In addition, a problem arises when a resin formulation, comprising the conventional epoxy resin and the reactive diluent, is cured—the resulting cured thermoset exhibits a decreased heat resistance. Heat resistance is an important property for cured thermosets which must meet certain commercial industry standards. For example, Germanischer Lloyd requires the cured thermoset to have a Heat Deflection Temperature of 70° C. or greater (ISO 75 Method A). The decreased heat resistance can be only partially compensated by including relatively costly cycloaliphatic amine curing agents in the formulation. Accordingly, epoxy resin formulations having low viscosity and good heat resistance after curing which do not require the use of cycloaliphatic amine curing agents are needed for vacuum resin infusion molding, especially for large parts such as wind turbine blades, generator nacelles and nose cones, which are made using the vacuum resin infusion molding process.
Divinylarene dioxides, such as divinylbenzene dioxide (DVBDO), are class of diepoxides which have relatively low liquid viscosity (for example less than 25 mPa·s at 25° C.) and high rigidity (for example less than or equal to 10 as measured by the calculated number of rotational degrees of freedom of the dioxide excluding side chains using the method of Bicerano (Prediction of Polymer Properties, Dekker, New York, 1993). The rigidity of divinylarene dioxides are higher than the conventional epoxy resins previously used in formulations for vacuum resin infusion molding. The resulting divinylarene-based formulations do not require the use of cycloaliphatic amine curing agents to obtain the required heat resistance. Therefore, it would be an improvement in the art to provide a divinylarene-based formulation useful for vacuum resin infusion molding.
British Patent No. GB 854679 describes the curing of DVBDO with polyfunctional amines; and Japanese Patent No. JP 62153316 describes compositions made from epoxy resins, curing agents, and hydroxyl-functional amines. Neither of the above two prior art references describes the use of polyaminoethers as a polyfunctional amine curing agent for DVBDO.
It is therefore desirable to provide a resin formulation for use in a vacuum resin infusion molding process which includes (a) a divinylarene dioxide, and (b) a polyaminoether.